When Morgana was young, she was liked less than Ursula by her mother. She also knows less magic than Ursula does. Morgana got criticized a lot for her jealousy of Ursula. Their mother soon died as revealed by Morgana when she, herself, usurped King Triton's throne, becoming queen herself. A picture of Ursula and Morgana's mother was seen in the deleted scene "Gonna Get My Wish". It is less likely she was banished from King Triton's kingdom like her sister, Ursula was, though.

The Party celebrating baby Melody's birth is interrupted by Ursula's revengeful sister Morgana attempting to prove her superiority over Ursula. She attempts to feed Melody to her shark, Undertow, but fails when Undertow is changed into a piranha and Prince Eric and Ariel rescue Melody. So, Morgana, Undertow, and her two manta rays, Cloak and Dagger leave inside a huge funnel. While Morgana leaves, she threatens to return and revenge everyone and Melody, mainly.

Morgana, Undertow, Cloak and Dagger now live in an iceberg lair. Morgana is now trying several attempts to change Undertow back into a shark but all fail. Morgana now believes that it is no use getting the trident and that trident is too powerful for her to overcome. It is soon revealed that Morgana does not like being criticized because all her mother ever did was criticize her and tell her she should be more like Ursula. It is also revealed that their mother favored Ursula more than Morgana. Morgana and Undertow argue about whose fault was what about hiding in the lair. The orb light shines and Morgana goes and sees Melody's hands holding the locket. They both get an idea. They will use Melody as the tool to Triton's undoing!

Morgana sees that her evil time has finally arrived when she sees Sebastian's failing attempts to stop Melody from going out to sea to find out the secret of the locket. So, she sends Undertow, Cloak and Dagger to lure Melody to her lair. The plan succeeds.

Morgana welcomes Melody to her palace and reveals the secret of the locket. She then, transforms Melody into a mermaid with Ursula's last magic potion that Morgana's been saving for a special occasion. After Melody's rejoicing has gone away, Undertow is angry that she didn't use the potion to change him back. Morgana tells Undertow to "keep his scales on" and that she's still reeling her in.

Melody arrives back to Morgana's lair to thank her. After Melody thanks her, Morgana plots by fake-crying. Morgana reveals that the mermaid spell is temporary. Morgana lies to Melody that "her" trident was "stolen" by a "deranged kleptomaniac" (she's referring to King Triton and his trident) and that "there is no one left to give it back for her". Melody tell Morgana that maybe she could get it back for her. Morgana acts surprised. She shows Melody the map and where the "scoundrel" lives. Melody asks if she means that it wasn't just "an ordinary fish tale" like her mother told her and if it really exists. Morgana says "Of course it exists. Whoever told you otherwise?" Melody tells Morgana that her mother did. Morgana responds that she's sure Melody's mother didn't mean to be cruel and deceitful. Melody says that she will bring back 'her' trident, and that she can count on her. Morgana says, "Be careful, dear! Enjoy those fins!" Then she says softly with an evil grin "while you can". She chuckles sinisterly.

Morgana sees Melody, Tip and Dash near Atlantica. Morgana sends Cloak and Dagger to go and make sure nothing interferes with Melody's return.

Ariel and Flounder have followed Cloak and Dagger to her lair. Just as Melody is about to give Morgana the trident, Ariel shows up and stops her, frantically. Melody is angry and shocked that Ariel hid the truth about her locket. Morgana and Ariel are trying to convince Melody to give the trident to each other. But, Melody, angry at Ariel for hiding the truth about her locket, gives it to Morgana. Morgana cackles and claims that all the seven seas are at her command. She grabs Ariel with her tentacles. Melody tries to stop her but Morgana stops her by pointing the trident at her. Morgana reveals that Ariel was only trying to protect her from her. Morgana confesses that she herself tricked Melody into giving the trident to her and that King Triton is really the king and is Melody's grandfather. Melody realizes the truth. Morgana blames Melody for the theft. Then, she imprisons Melody and Flounder into a part of her lair. She tells Melody that her time as a mermaid has just expired. Morgana then takes Ariel with her.

Morgana rises to the roof of her own lair on top of her new cliff. Prince Eric, his crew, and Scuttle arrive to battle the now-powerful sea witch. However, Morgana destroys Prince Eric's boat. Prince Eric and his crew are forced stand on the ice and they survive. King Triton, his guards, and Sebastian arrive to battle the now-powerful sea witch as well. Morgana dares King Triton to hurt her and then cackles. After Undertow taunts Triton, Sebastian chases Undertow, angrily but Morgana transforms Undertow into a gigantic shark and Sebastian manages to flees. Prince Eric takes his sword out and asks, angrily, where's Melody and what has she done with her. Morgana replies "Oh you wanna join your daughter? Well, I think that can be arranged" She commands Cloak and Dagger to take Prince Eric to Melody underwater to drown. Scuttle distracts Morgana and Ariel is free and she and Sebastian rescue Prince Eric, while Tip and Dash defeat Undertow and rescue Melody. Sebastian defeats Cloak and Dagger.

Morgana forces all the creatures she sees to bow down to her. Melody realizes that she has to get the trident herself since Ariel, Tip and Dash are forced to bow down to Morgana, and Prince Eric is unable to help because he is unconscious. Melody realizes that she has legs and that power of Morgana cannot harm her. Morgana then forces King Triton to bow down. Morgana looks up at the sky and says to her mother that she has finally won. As Morgana sentences King Triton to oblivion, Melody surprises Morgana by snatching the trident from her. Morgana, eventually tries to take the trident away by tying up one of Melody's feet, she lifts Melody upside down and tries to grab the trident back, but Melody pierces the trident through one of her tentacles, distracting her. and Melody is free. Melody gives the trident back to Triton.

Morgana pushes Melody off the cliff after she throws the trident to Triton, but Dash saves Melody. Triton grabs his trident, says to Morgana, "Never will you or yours threaten my family again. There will be no escape for you! Ever!" and imprisons Morgana in a small iceberg. and she sinks. Still alive while she sinks, she whimpers "Mommy!" because she realizes that she has failed her mother by being defeated. The picture of Ursula sinks along with her, a little far behind.

Morgana is as cruel as her own sister. She shows that she hates being criticized in the movie when she berates Undertow. Morgana is deceitful, baleful, and ruthless. She wants to steal the trident to prove her superiority over her sister. She lacks her sister, Ursula's, deviousness. She also is not as good as using potions as her sister does as shown when Morgana fails all attempts to turn Undertow back into a shark. Morgana is shown to have a funny sense of humor, such as at the beginning when she grabbed Eric's advisor, Grimsby and said "Now, is that fair Gramps, I ask you". She tickled Grimsby chin with her fingers and with a nice smile. She then says "But then whoever said we had to play fair?" Though Morgana's personality is different she does have the same objective as Ursula. Many people think she was less interesting Ursula.

Morgana appears very thin, closer to a squid than an octopus. She is younger than her sister, and her skin is green hue. Despite this, Morgana looks older than her sister (this may be due to how much time has passed). Morgana's octopus arms are green instead of purple like Ursula's.